Most types of protective headgear worn by workers to protect them from falling objects are held on the worker's head by a suspension system. The suspension system, along with the helmet itself, act to absorb the shock of a falling object striking the worker's head. The suspension system is also used to hold the helmet on the worker's head.
The suspension is often a web-like support system comprising two or more strips of material that are arranged to cross each other. The ends of the strips are, for example, attached at four or more points around the interior circumference of the helmet. A band is then attached to the four or more points of the suspension to permit the helmet to be worn by the worker. To securely position the helmet on the worker's head, it is essential that the circumference of the headband be adjustable to fit the appropriate head size. A napestrap is often attached at one end of the band to achieve these results.
In the Staz-On.RTM. Suspension, currently available from Mine Safety Appliances Company of Pittsburgh, Pa., and described in U.S. Pat. No. 3,500,474, the disclosure of which is incorporated herein by reference, an adjustable napestrap is manually adjusted by the wearer. The two ends of the napestrap are connected and held in place by a slot-and-teeth arrangement. One end of the napestrap is formed with parallel rows of teeth. The other end of the napestrap is formed with parallel rows of slots. The size of the suspension can be adjusted by inserting the teeth of one end of the strap into the slots formed in the other end of the strap at the desired length.
The Fas-Trac.RTM. Suspension, currently available from Mine Safety Appliances Company of Pittsburgh, Pa., and described in U.S. Pat. No. 4,942,628, the disclosure of which is incorporated herein by reference, has an adjustable napestrap wherein the ends of the strap are connected, held in place, and adjusted by a ratchet mechanism. The ratchet mechanism generally operates on a gear-and-teeth or rack-and-pinion arrangement. The adjustment knob of the ratchet mechanism has attached to it at one end a set of cog teeth. These teeth are positioned inside a lateral section of the napestrap. The lateral section of the napestrap has rows of teeth formed along the inside of slots therein. By placing the cog teeth in contact with the slot, the size of the napestrap can be adjusted by turning the knob one direction to pull the strap ends closer together or turning the knob the other direction to force the ends apart. A spring-activated detent mechanism is typically included to resist undesirable rotation of the adjustment knob.
In general, the ratchet-type suspension is preferred over the slot-and-teeth suspension because the ratchet-type suspension generally can be adjusted more easily while on the head of the worker. There are, however, certain disadvantages to ratchet-type suspensions. For example, ratchet suspensions often have numerous component parts that must be assembled to operate the ratchet. The number of parts and the labor required to assemble the parts is quite costly. Moreover, metallic parts must often be avoided to reduce the risk of electrical shock to workers exposed to electrical wires or equipment.
Finally, ratchet-type suspensions sometimes do not prevent loosening of the headband after the user has adjusted the headband to the size of the user's head. In that regard, during normal use, protective headgear often experiences forces that tend to expand the size of or loosen the headband. Unless the ratchet mechanism provides suitable resistance to such forces, the headband will loosen, requiring constant adjustment by the user.
It is, therefore, desirable to provide an adjustable headband with a ratchet mechanism that is inexpensive to make and assemble and can be easily tightened, while still providing adequate resistance to loosening of the headband during use thereof.